Fenestration refers to products that fill openings in a building envelope, such as windows, doors, skylights, curtain walls, etc. These products are designed to permit the passage of air, light, vehicles, or people. A building envelope, in turn, generally refers to the separation between the interior and the exterior environments of a building. As such, the building envelope serves as an outer shell that both protects and facilitates climate control of the indoor environment.
During daylight hours, people typically draw blinds to reduce or eliminate the glare caused by the sun light piercing through a window. This blocks a substantial portion of the view from the window, and thereby defeats the purpose of having a window in the first place. As a result, there has been an effort to modify a window by directly applying on it a glare-reducing film that is transparent enough to not obscure the view through the window.
FIG. 1 shows a modified window 10 including a surrounding frame 14, secured within which is a window 12. According to this figure, a glare-reducing film 16 directly attaches to an interior surface of window 12. The term “interior surface,” as used in this specification refers to the surface which is inside the building envelope. Furthermore, a combination of a film (e.g., glare-reducing film 16) directly attached to a window (e.g., window 12) is hereinafter referred to as “a window/film combination.”
Glare-reducing film 16 commonly includes aluminum, which is incorporated into the film matrix by either well-known sputtering or vapor deposition methods. An exemplar of such a film is Silver 35, which is commercially available from 3M Corporation of Minneapolis, Minn. The incorporated aluminum composition in this film reflects a certain amount of light (e.g., about 35%) impinging upon the window/film combination. The film is also designed to reflect a certain amount of heat (e.g., between about 30% and about 50%) that strikes the interior surface of a window.
When using glare-reducing films, a certain amount of light (e.g., sun light) that impinges upon a window/film combination reflects back to the exterior of the building. During summer season, greater reflection of light keeps out greater amount of heat associated with that light from the building's interior and allows cooler temperatures to prevail inside the building envelope.
Similarly, a certain amount of heat that is contained in an interior of a building envelope reflects back by a window/film combination. During winter season, greater reflection of heat allows a greater amount of heat retention inside the building's interior and allows for warmer temperature to prevail inside the building envelope.
Unfortunately, directly applying a film to the interior surface of a window, as conventional designs propose, suffers from drawbacks. Specifically, the amount of light and heat that is reflected does not rise to the desired high levels to be considered energy efficient. In fact, the conventional window/film combinations absorb a greater than desired amount of light impinging upon it or greater than desired amount of heat contained inside the building envelope.
Significant amount of light that is absorbed by a window/film combination is converted to heat. Thus, regardless of whether heat or light passes through a window/film combination, in both cases ultimately heat is absorbed heat by the window/film combination. In other words, during summer season, a conventional window/film combination absorbs and transmits to the building interior a greater amount of heat than is desirable, and during winter season, heat losses through a conventional window/film combination are greater than desirable. In both seasons, the amount of heat absorbed by the conventional window/film combination places an excessive load on an air-conditioning unit which is working to regulate the temperature inside the building envelope.
What are therefore needed are energy-efficient systems and methods which reduce the load on air-conditioning units regulating the temperature inside the building envelope.